This invention relates to a bicycle free wheel hub with a coaster brake adapted to be actuated by back-pedalling.
There have been proposed various models of the coaster hubs, among which the most relevant prior arts to the present invention are disclosed in specifications of U.S. Pat. No. 3,252,551 and Japanese Patent Application Laying-Open No. 50-8,237.
As illustrated in FIGS. 7 and 8 of the accompanying drawings, the first model of the prior art device proposed in said U.S. patent comprises a fixed axle a, a driving member b journalled thereon, an anchor member c non-rotatably mounted on the axle a, hub shell g journalled on the driving member b and anchor member c and having an interior cylindrical braking surface d and an interior frusto-conical clutch surface e engageable with a corresponding clutch surface e' of a clutch nut h, said driving member b having a threaded portion f extending into the interior of the hub shell g, the clutch nut h being threaded on the driving member b for traversal into and out of engagement with the interior clutch surface e of the hub shell, and an expander member j loosely located in the hub shell g between the clutch nut h and anchor member c, said expander and anchor members having frusto-conical sleeve portions i, k extending toward each other, a pair of substantially semicylindrical brake shoes 1 resting at their ends on the conical portions i, k of the expander and anchor members j, c, said expander and anchor members having diametrically located projections n, n' extending radially from the conical portions i, k thereof and located between the brake shoes 1 to thereby prevent rotation of the brake shoes and of the expander member, said clutch nut h and expander member j having clutching teeth o, o' adapted to prevent relative rotation when engaged, a detent sleeve m frictionally engaging the clutch nut h and expander member j to insure traversal of the clutch nut h responsive to rotation of the driving member b, and said projections n, n' from the expander and anchor members j, c having substantially radial side surfaces which remain in contact with the surfaces of the members j, c from which they have been partially severed to thereby support the projections against torsional stress.
According to this first model, however, the expander member j and the clutch nut h must be provided as separate pieces in addition to the fact that it is necessary to provide the detent sleeve m having such a configuration, substantially as illustrated in FIG. 8, resulting in such a disadvantage that the high manufacturing cost cannot be avoided because of relatively large number of parts requiring complicated manufacturing processes. A further disadvantage is that, since the detent sleeve m is adapted to embrace and bear with a strong friction on the cylindrical surfaces of the expander member j and the clutch nut h, undesirable frictional heat is developed therebetween to a considerable degree when the driving member b is rotated in the forward direction. A still further disadvantage is that, when the driving member b is rotated in the back-pedalling direction, there occurs an undesirable slip between the expander member j and the detent sleeve m, hindering a quick braking function.
In order to overcome some of the disadvantages inherent in the afore-said first model, an improved type, that is, the second model as illustrated in FIG. 9, is proposed in said laid-open Japanese patent application, wherein the expander member j and clutch nut h in said U.S. patent are combined into a single piece of clutch cone q, and the sleeve m in said U.S. patent is replaced with a left-handed coil spring p, being characterized in that the coil spring p, which has an external diameter equal to or slightly smaller than the internal diameter of the clutch cone q, is fixed at one end to a fixed brake cone c' (corresponding to said anchor member c) and partially received at a position r within the clutch cone q having right-handed threads formed internally thereof and screwed on a cylindrical extension of a driving member b', so that, when the driving member b' is rotated in the back-pedalling direction, said coil spring p is forcibly expanded in diameter to impart such a great frictional resistance to the internal surface of the clutch cone q as to permit integration of the two elements p, q, causing thereby relative rotation of the driving member b' with respect to the clutch cone q, and as a result, the cone q is moved axially by threads in the leftward direction of FIG. 9 to come into frictional engagement at opposed tapered surfaces s with the brake shoes 1.
Although this second model of the conventional device can be manufactured at a lower cost as compared with the aforementioned first model, it is still disadvantageous in that an undesirable slip occurs between the clutch cone q and the coil spring p and that a certain time is required until the coil spring p has been deformed enough, hindering a quick braking effect. A further disadvantage is that it cannot be dispensable to provide a certain detent means (not disclosed) performing the same function as said projections n, n' of the foregoing first model in order to prevent the relative rotation between the brake shoes 1 and the brake cone c', resulting in that an increased cost working process for forming said detent means is required. A still further disasdvantage is that repeated expansions and torsions of the coil spring p easily invite fatigue thereof and deterioration in performance. In other words, this second model is inferior in durability.
It is an object of the present invention to eliminate the above-discussed disadvantages inherent in conventional devices.
Another object is to provide an improved bicycle free wheel hub with coaster brake which is simpler in construction and smaller in number of parts, thereby permitting a lower manufacturing cost.
A further object is to provide an improved bicycle free wheel hub with coaster brake which facilitates quick and accurate braking effect.
A still further object is to provide an improved bicycle free wheel hub with coaster brake which can enjoy a long span of life without deterioration in performance.
According to the present invention, there is provided a free wheel hub with coaster brake comprising an anchor member having a pair of axial slits formed in diametrically opposite sections thereof, a pair of detent pieces which are formed separate from the anchor member so as to be received within said slits of the anchor member, each of said detent pieces being provided with a contact surface which frictionally prevents the rotational movement of the brake shoes, each of the detent pieces being further provided with a reduced extension which is engageable with an internal non-smooth contact surface of a clutch cone, and a spring member adapted to urge the reduced extensions of the detent pieces against the internal non-smooth contact surface of the clutch cone. The non-smooth contact surface may be formed in various ways as will be hereinafter described in detail with reference to the accompanying drawings.